This invention relates to the production of particulate sulfur and, more particularly, to a method and apparatus for transforming molten sulfur into solid particles of controlled size.
Solid particulate sulfur has many industrial and agricultural applications. The desired particle size depends upon the particular application. For example, sulfur spread on soil by a mechanical spreader typically would have a particle size that will pass a 20 mesh Tyler screen, and sulfur employed for insecticides or rubber production typically would have a particle size that will pass a 325 mesh Tyler screen.
The conventional way to produce sulfur in particulate form is to pour molten sulfur on a concrete slab or a water cooled metal or rubber conveyor belt, thereby forming a solidified layer of sulfur, which is broken up into lumps or flakes by mechanical means such as a crusher or bucket loader. Before reducing the lumps or flakes to the desired fine particle size, they must be aged for a substantial period of time, e.g., from three to nine months, to develop a concise rhombic crystal structure that will be suitable and resist coalescing under the pressure of the mechanical milling required to produce the desired particle size.
Soil sulfur can be produced by feeding the lumps or flakes into a variety of crushers or mills. Sulfur in a form suitable for insecticides is generally produced by feeding aged sulfur particles into a roller mill. The milling operation is expensive, hazardous, and slow. To prevent explosions, the milling operation is carried out in an inert atmosphere such as combusted natural gas with an oxygen content reduced to about 3%. To prevent the particles of sulfur from coalescing due to the energy being expended, the temperature of the inert atmosphere during the milling operation must also be closely controlled by recycling through coolers and the like.